staging: comedi: vmk80xx: wait for URBs to complete

For Velleman K8055 (aka VM110), `vmk80xx_read_packet()` and
`vmk8055_write_packet()` send an URB asynchronously and do not wait for
it complete.  However, callers of `vmk80xx_read_packet()` are assuming
the contents of the data buffer `devpriv->usb_rx_buf` are valid
immediately after that function returns.

For Velleman K8061 (aka VM140), `vmk80xx_read_packet()` and
`vmk80xx_write_packet()` punt the requests to `vmk80xx_do_bulk_msg()`
which *does* wait for the URBs to complete (albeit with no error
checking!).

Change `vmk80xx_read_packet()` and `vmk80xx_write_packet()` to use
`usb_interrupt_msg()` for the K8055, so the callers of
`vmk80xx_read_packet()` can assume the data buffer contents are valid
(if no error occurred).  Remove all the code for checking for transfers
in progress and busy waiting, as it's no longer needed.  Pretty much all
the callers of `vmk80xx_read_packet()` and `vmk80xx_write_packet()` hold
the same semaphore anyway, and the only caller that doesn't
(`vmk80xx_reset_device()` called during initialization of the device)
doesn't really matter.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>